This invention relates to hydraulic pumps and more particularly to the means of handling of the fluid returned to the hydraulic reservoir used to feed the pump under high flow, high pressure conditions with low noise.
Fixed and/or variable positive displacement hydraulic pumps have numerous applications in many fields, including automotive, aerospace, industrial, agricultural, heavy equipment and the like for performing work. In a typical hydraulic system, return fluid is simply returned into the pump reservoir where it dwells for a time period before being drawn in by the inlet to the pump for recirculation. Under conditions of high load and high flow rate, such hydraulic systems are characteristically unable to keep up with the fluid demand of the pump, leading to cavitation and unacceptable levels of noise. Another inherent disadvantage with such systems is that the kinetic energy of the incoming fluid to the reservoir is lost and not utilized to feed the inlet to the pump, leading to relatively low efficiencies. Such simple single return hydraulic fluid return systems thus have their limits.
U.S. Pat. No. 5,802,848 discloses a hydraulic steering system for a motor vehicle having two separate fluid return lines leading to the reservoir. One line is a high return flow which is fed to a nozzle within the reservoir. The outlet of the nozzle is supported adjacent the inlet to the steering pump. The momentum of the return fluid exiting the nozzle creates a venturi action at the reservoir outlet, which has the beneficial effect of aspirating additional volumes of fluid from the reservoir. The momentum of the return fluid together with the addition of the entrained fluid from the reservoir produces a desirable xe2x80x9cboostxe2x80x9d effect which provides ample feed to the pump under conditions of high flow and high pressure to prevent cavitation attributable to lack of sufficient inflow to the pump. The second return line delivers a fraction of the return fluid to the reservoir. Such fluid is permitted to dwell for a time in the reservoir chamber, during which time any undissolved air or gas bubbles contained in the secondary stream are liberated before the fluid is drawn in by the primary jet stream. Without the secondary return line, the fluid would not be sufficiently deaerated and cavitation and noise would result.
One inherent limitation of the above system is that it requires two separate return lines to the reservoir, and thus may not be suitable for all pump applications, and particularly those having only a single high flow return line. The requirement of the secondary line further adds cost, weight and complexity to the construction of the system and particularly the reservoir.
A hydraulic system according to the invention includes a hydraulic pump reservoir having a fluid outlet communicating with the inlet to the pump, a single fluid return line having a nozzle within the reservoir adjacent the outlet and operative to direct a high velocity jet flow of fluid from the single return line into the outlet and to thereby aspirate additional volumes of fluid into the inlet to achieve high flow, high pressure operation of the pump. According to a characterizing feature of the invention, the nozzle includes at least one bleed hole through which a fraction of the fluid flow escapes into the reservoir at a location upstream of the nozzle outlet and dwells for a time sufficient to liberate any entrained air or gas bubbles before being drawn into to the pump by the primary flow stream.
The invention has the advantage of achieving, with a single return line, high velocity, high flow delivery of fluid to the pump while deaerating the fluid to minimize cavitation and noise.
The invention has the further advantage of being readily adaptable to any hydraulic pump system calling for high velocity, high flow delivery of fluid to the pump with low noise, whether the system has a single or multiple return lines. According to the invention, multiple return lines can be converged upstream of the reservoir to provide a single high flow return line leading to the reservoir. Some of the systems contemplated by the invention include, but are not limited to vehicular power steering, transmission, and engine oil applications; industrial; construction; heavy equipment; aerospace, etc.
The invention has the further advantage of eliminating the need and thus cost and added weight of a secondary flow return line, as is necessary with system of the above-mentioned ""848 prior patent.